1. Field of the Invention
The present invention relates to a method and apparatus for controlling a drum-type washing machine, and more particularly, to a method in which, before entry into a main dewatering phase of a dewatering process performed by a controlled spinning of a drum driven by a motor, the motor speed is maintained for a predetermined time at a rotating speed below a resonance range.
2. Discussion of the Related Art
In a drum-type washing machine, laundry placed in a rotatable drum accommodating washing water is washed using a friction generated between the laundry and drum when the drum is rotated by a driving force, to obtain a washing effect by beating and rubbing the laundry. Drum-type washing machines are advantageous in that tangling and damage to the laundry are minimal. FIG. 1 illustrates a direct-coupling drum-type washing machine as an exemplary apparatus according to a related art.
Referring to FIG. 1, a drum shaft 13, coupled to a drum 9 that has a plurality of lifts 14 attached to an inner surface and is rotatably installed in a tub 3 housed within a cabinet 5, transmits a driving force to the drum from a motor 6 including a stator 7 and a rotor 8 provided at the rear of the drum. To facilitate drum rotation, a set of bearings 12 in contact with opposite ends of the drum shaft 13 is supported in a bearing housing centrally disposed on a rear wall of the tub 3. The stator 7 is fixed to the rear wall of the tub 3, and the rotor 8 is fixed to the drum shaft 13. Thus, the drum 9 is directly coupled to, and rotated by, the rotor 8.
A gasket 2 is provided between the tub 3, and a door 1 installed in the front of the cabinet 5. The tub 3 is suspended on springs 4 hanging from within the cabinet 5 and is supported by a damper 10 having opposite ends respectively connected the tub and cabinet. During a dewatering process, which is performed by a high-speed rotation of the drum 9 while the tub 3 is full of water for repeated steps of a wash course, vibration is generated in the gasket 2 and, more importantly, in the tub. Therefore, drum speed is controlled by detecting a rotating speed of the rotor 8 using a motor sensor 11, such as a Hall sensor or the like, attached to one side of the motor 6. Throughout dewatering, a drain pump 15 is activated to expel from the washing machine all the water contained in the tub 3 and to extract, by simultaneously spinning the drum 9, a maximum amount of the water absorbed into the laundry in the drum.
A controller 16, including a microprocessor with memory, is installed behind a control panel on a forward surface of the cabinet 5 to enable access and operation by a user. The dewatering process is performed according to an algorithm stored in the memory and executed by the microprocessor according to an amount of laundry in the drum 9 as detected at the beginning of a wash cycle, which is part of a wash course selected by the user via the controller 16.
A contemporary dewatering process will be described with reference to FIGS. 2 and 3.
Upon initiation of a dewatering cycle, the drain pump 15 is activated and water begins to drain from the tub 3, reducing the load accordingly. The motor 6 is accelerated (S307) to a first rotating speed for eccentricity detection (S308), and this eccentricity detection speed is maintained while a state of balance or imbalance (eccentricity) in the rotating drum is determined. Assuming that the detected eccentricity falls within a nominal range (S309), the motor 6 is accelerated further to a second rotating speed for extracting water from the laundry; otherwise, the drum rotation is paused (S320) so that the steps S307 and S308 can be repeated for a slightly reduced water load. It should be appreciated that each instance of eccentricity detection is countable during the execution of the wash course algorithm, so that the dewatering process may be performed according to an updated counter value (n) of, say, n=1, 2, or 3 (S310).
Upon reaching the second rotating speed (S311), the rotational speed of the motor 6 is immediately reduced (S313) to the first rotating speed for eccentricity detection to be again performed. Assuming that the detected eccentricity again falls within an expected (nominal) range, the counter is updated, and the rotational speed of the motor 6 is increased to a third rotating speed (S314), which is higher than then second rotating speed, after which the motor speed is again reduced to the first rotating speed (S315) for another eccentricity detection. Here, too, as soon as the higher rotating speed is reached, the rotational speed of the motor 6 is immediately reduced to the eccentricity detection speed, i.e., the first rotating speed.
After completing the above sequence of eccentricity detections, and assuming the rotating drum's state of balance falls within an acceptable range, the dewatering process enters the main dewatering phase (S316), whereupon the rotational speed of the motor 6 is increased to a maximum rotating speed set according to the amount of laundry detected at the beginning of the wash cycle. Throughout the dewatering process, the drain pump 15 continues to pump water from the tub 3, extracting more and more water, thereby reducing the load of the spinning drum and lowering its detected levels of eccentricity as determined by the microprocessor of the controller 16, which periodically senses load variations exerted on the motor 6. At the same time, i.e., as the amount of water in the tub 3 is being reduced, the cycling of the drum speed promotes a settling (even distribution) of the laundry in the drum 6. It should be appreciated that the main dewatering phase may be entered after any number of eccentricity detections provided that an acceptable level of eccentricity has been reached.
In the dewatering process as described above, however, the immediate reduction in drum motor speed upon reaching an accelerated speed, e.g., the second or third rotating speed, provides insufficient time for appreciable water extraction. This problem is exacerbated when the laundry includes materials capable of retaining greater amounts of water and can lead to dewatering times of five minutes or longer, since the amount of water in the laundry, and in turn the load of the motor 6, is nearly the same for the next acceleration, which unnecessarily prolongs the dewatering process by delaying entry to the main dewatering phase. Furthermore, the higher loads produces a sharp rise in eccentricity for the ensuing stage of drum motor acceleration, generating undue noise levels caused by the tub 3 striking an interior surface of the cabinet 5 and an excessive twisting of the gasket 2, and may even result in a “walking” phenomenon in the washing machine. These drawbacks are particularly troublesome as the drum motor is accelerated to the second or third rotating speed to pass through a rotating speed at which resonance occurs, without considering the sharp rise in eccentricity, which is due to the drum motor speed being reduced to the eccentricity detection speed too soon after an accelerated state.